Herbaceous Perennials | Autumn Gardening Tasks

Herbaceous perennials – the term just rolls off the tongue!

In the late September and October flower garden, you’re likely to still have lots of flowering plants. And herbaceous perennials will be the plants that are giving you most of those flowers. They’ll be providing colour through foliage too.

Herbaceous Salvias, Helenium, Helianthus and Japanese anemones keep flowering and looking good right through October. Not forgetting Heuchera for foliage.

So you’re looking at your Heuchera ‘key lime pie’ with all its zingy limegreen foliage. Perhaps you’re thinking, “I’d like some of that in the front garden; I must remember to another one next year”?

Maybe you love your Japanese anemone with its soft pink flowers but you’re sighing. “it’s a bit big for that space; I’ll have to get rid of it”?

As all of these flowering plants are herbaceous perennials, it is possible to enjoy them year after year. But there is a little work is involved. Satisfying work and economical as you’ll be gaining more plants for nothing more than a bit of gardening. Among your autumn gardening tasks you can include increasing your stock of these useful plants.

Different types of Herbaceous Perennials

Herbaceous Perennials include a wide range of both flowering and foliage plants. They can be categorised according to how frost hardy they are. For example: –

Hardy – such as Japanese anemone, Heuchera
Half-hardy – such as Heliotrope (cherry pie), Gaura
Tender – such as Verbena rigida, Plectranthus

Lifting, splitting and dividing Herbaceous Perennials

Firstly, prune back the stems to about 4” or 10 cm high, cutting above a bud; do this whilst there is still some foliage on the plant.
You may be able to use some of these as cuttings to increase your supply of plants, although taking cuttings is best done during the spring and summer.
Then lift (dig up) the plant with a decent root ball

Tender Herbaceous Perennials

These usually require frost-free conditions, but may survive outdoors in certain micro climates, such as those found in the city centre gardens. Even if the frost kills off the foliage to ground level, they may re-grow from below ground the following spring. However, in colder and wetter areas, it’s probably a safer option to store your tender plants in pots, in a cool frost free greenhouse, conservatory or shed.

Put into a pot, not too much bigger than the root ball, but so it’s not squashed.
Give it a good watering at this point, but reduce the watering over the winter as it will be semi dormant.
Keep in a frost free environment

Half-hardy Herbaceous Perennials

These perennials should over winter fine if they’re planted in free draining soil and not subject to too much wet and long periods of cold.
Taking cuttings in late summer is a good back up plan.
Laying mulch around will keep the roots safer from frost, so in milder areas this is worth doing.
If the weather does turn very wet or cold, you could lift and treat as the tender perennials (above).

Hardy Herbaceous Perennials

Now, what about that Japanese anemone that’s elbowing out other plants in the border and the Heuchera you’d like more of? It’s an easy process to lift and divide hardy perennials such as these. The Heuchera, along with Alchemilla mollis, Geraniums and so on, respond well to division at this time of year.

Dig up the plant you want to split and have a look at how it increases its size. The root system is most likely to be made up of many fibrous roots rather than one thick root. Tease away some of the side pieces, being sure that they have both root and leaf on each piece you’re taking. If there’s only a small amount of root you may want to dip them in some hormone rooting powder; certainly it’s a good idea to reduce the amount of foliage on the ‘baby’, to reduce stress.

Then either pot the newly separated plants up into well-draining compost or plant in another area of your flower border or garden. The soil is still warm from the summer, so dividing and moving hardy herbaceous plants now means they have the right conditions to settle into the border soil before the winter cold. Replant the parent plant and give all of the plants a good watering in.

The Japanese anemone can be divided in the same manner, but I have to admit that if it’s still flowering profusely I might be tempted to wait until spring. Late flowering hardy herbaceous perennials have plenty of time during spring and early summer to settle in and put on new leafy growth and form flowers.

If you run out of time to lift and divide herbaceous perennials this autumn, you can carry out this gardening task in the spring. If you’d like guidance on which plants in your garden would be suitable to lift and divide ask about our Garden Advice Visits.

Or if you’d like to learn about lifting and dividing herbaceous perennials and other seasonal tasks in your garden, Plews offers 1-2-1 Gardening Lessons where your garden is the classroom. You may like to read about some of the things you could do in a garden lesson.